The ownership structure of Unity Trust Bank – which provides loans to the Labour party – is to be overhauled as a result of the Co-operative Bank's 27% stake being put up for sale.

The trade unions that own the remaining 73% of Unity Trust have the right to buy any shares sold by the Co-op Bank, which is itself being overhauled under the new management team that led last year's £1.5bn rescue deal.

Set up in 1984, Unity Trust is best known for providing banking services to trade unions, charities and local authorities.

Graham Bennett, who chairs the Birmingham-based Unity Trust, said detailed discussions were underway to "reposition the bank as we approach our 30th anniversary".

"The Co-operative Bank has been a fantastic supporter of Unity Trust since it was first founded, however, the time is now right to review our structure as we begin the next chapter of Unity's development underpinned by our distinct approach to banking," said Bennett.

Co-op Bank is facing sweeping job cuts as its new chief executive Niall Bookers attempts to restore profitability following the capital shortfall which led to the rescue by its bond holders – led by US hedge funds – and resulted in the Co-op Group of supermarket, pharmacies and funeral homes ceding control of the bank. It was also hit by the scandal surrounding its former chairman Paul Flowers who is alleged to have bought illegal drugs.

Booker said: "The Co-operative Bank has been a proud supporter of Unity Trust over many years and we will work closely with them through this process, which fits with our own business plan to simplify the bank."